(4hm) 3D-Printed Zeolite 13X Gyroid Monolith Adsorbents for CO2 Capture

The global challenge of climate change, driven predominantly by the rise in atmospheric carbon dioxide (CO₂) levels owing to human activities, requires effective CO₂ mitigation strategies^1,2. This study investigates the fabrication, characterization, and performance assessment of self-standing 3D-printed gyroid monoliths of zeolite X for CO₂adsorption. Leveraging digital light processing (DLP) 3D-printing technology, monolithic structures with precise control over cell size and relative density were fabricated using a slurry comprising a commercial photopolymer resin and zeolite X powder. Post printing, debinding and sintering steps (at temperatures of 550, 700 and 800 °C) were employed to remove the polymer binder and achieve the structurally integral zeolite X monoliths. The resulting monoliths were subjected to physical and structural characterization and adsorption tests to elucidate their potential for CO₂ capture applications. Structural and morphological analyses, including optical microscope and scanning electron microscopy (SEM) imaging, revealed the interconnected gyroid cells within the monoliths, facilitating efficient gas diffusion and enhanced surface area accessibility. The 3D-printed samples exhibited a highly porous structure with well-defined channels and interconnected pores, which are conducive to effective gas adsorption. 3DPZX-550, the monolith sintered at 550 °C, exhibited a CO₂ adsorption capacity of 3.88 mmol/g comparable to zeolite X beads (4.07 mmol/g) at 25 °C. Mechanical strength evaluations through compression tests demonstrated the suitability of 3DPZX-550 for CO₂ capture application, with a compressive strength of 0.24 MPa. During CO₂ adsorption kinetics evaluation at 25 °C and up to 1 bar, 3DPZX-550 reached adsorption capacity of 3.5 mmol/g in 77 min, whereas the parent beads and powder required 96 and 100 min, respectively. Additionally, heat of adsorption analysis revealed favorable regeneration energy requirement, with heat of adsorption values ranging from 22 to 33 kJ/mol for 3DPZX-550. The CO₂/N₂ selectivity at 25 °C ranged from 328 (at 50 mbar) to 51 (at 1 bar) for 3DPZX-550 whereas, the powder sample exhibited selectivity values in the range of 294 (at 50 mbar) to 33 (at 1 bar). Dynamic breakthrough experiments using CO₂/N₂ mixtures confirmed the fast kinetics with normalized CO₂ breakthrough time of 730, 763, and 1059 s/g for 3DPZX-550, powder, and beads, respectively, at 25 °C. The pressure drop in the 3DPZX was also significantly lower (14.5 Pa/cm at 20 ml/min to 267 Pa/cm at 50 ml/min) than both zeolite X beads (134 Pa/cm at 20 ml/min to 446 Pa/cm at 50 ml/min) and powder. The monolith with unique gyroid sheet lattice of curved channels in the direction of gas flow, along with large voids provided sufficient adsorbent/adsorbate contact with reduced breakthrough time yet with comparable pseudo equilibrium CO₂ adsorption capacity to that of beads and powder. The enhanced kinetics, separation performance along with lower pressure drop, and enhanced cyclic stability of the developed zeolite X gyroid monoliths hold promise in the development of efficient and sustainable structured CO₂adsorbents. Further efforts should focus on tuning gyroid cell size, TPMS lattice geometry, and optimizing gas flow rates toward application in large-scale systems.